EP3134622A1

EP3134622A1 - Catalyst subassembly, device comprising same for purifying exhaust gases from an internal combustion engine, modular system for the subassembly, and method for manufacturing the subassembly

Info

Publication number: EP3134622A1
Application number: EP15710495.1A
Authority: EP
Inventors: Hans-Juergen Bruene
Original assignee: Bayerische Motoren Werke AG
Current assignee: Bayerische Motoren Werke AG
Priority date: 2014-04-22
Filing date: 2015-03-18
Publication date: 2017-03-01
Anticipated expiration: 2035-03-18
Also published as: DE102014207530A1; EP3134622B1; US20170037755A1; WO2015161960A1; US10107162B2; CN105899773B; CN105899773A

Abstract

A catalyst subassembly (20) for a device for purifying exhaust gases from an internal combustion engine, in particular a diesel engine, comprises an SCRF catalyst (26) and an SCR catalyst (24) upstream of the SCRF catalyst (26), the two catalysts being arranged in a common catalyst housing (28). The catalyst housing (28), the SCRF catalyst (26) and the SCR catalyst (24) can be selected from a modular system for different variants of the internal combustion engine.

Description

The invention relates to a catalyst assembly for an apparatus for purifying exhaust gases of an internal combustion engine, in particular of a diesel engine, having a regenerable particulate filter and a device for cleaning the exhaust gases of an internal combustion engine the particulate filter integrated catalyst for the selective reduction of nitrogen oxides (SCRF catalyst). The invention further relates to a modular system for the catalyst assembly, a device containing the catalyst assembly and a method for producing the catalyst assembly.

For purifying the exhaust gases of modern motor vehicles, in particular of diesel vehicles, usually catalyst arrangements of a combination of oxidation catalyst or NOx storage catalyst and particulate filter are used. The oxidation catalysts arranged close to the engine and particle filters are generally installed in a common housing. To comply with stricter exhaust emission limits, the oxidation catalyst can be replaced in the same space by a NOx storage catalyst.

In the oxidation catalyst, carbon monoxide and volatile hydrocarbons are oxidized to carbon dioxide. The oxidation catalyst usually consists of a metallic or ceramic carrier substrate with a catalytically active coating of platinum group metals such as platinum and / or palladium. Since the exhaust gas temperatures of a diesel engine are significantly lower than the exhaust gas temperatures of a gasoline engine, oxidation catalysts for diesel engines (DOC) are preferably installed in the exhaust manifold near.

As regenerable particle filters, wall-flow filters and bypass filters can be used. With the wall-flow filters soot particles and others in the Exhaust flow existing solids fixed to a porous filter wall by adhesion. If the exhaust backpressure reaches a predetermined threshold due to particulate inclusions, regeneration of the particulate filter is initiated. For this purpose, for example, a post-injection of fuel into the exhaust gas flow can be carried out in order to increase the exhaust gas temperature and to burn the soot particles stored in the filter. With bypass filter technology, part of the exhaust gas flow is deflected and passed through a fleece layer. In this case, the soot particles are filtered out. Usually, secondary flow filters undergo continuous regeneration. For heavy vehicles, the catalytic converter arrangement of oxidation catalytic converter and particle filter can additionally be supplemented with an SCR catalytic converter. Selective catalytic reduction (SCR) refers to the selective catalytic reduction of nitrogen oxides (NOx) from combustion engine exhaust gases. Such an SCR catalyst is described, for example, in EP 1 203 61 1 B1 or EP 1 837 494 B1.

For the operation of the SCR catalyst, a reducing agent for the nitrogen oxides, for example an aqueous urea solution commercially available as "AdBlue ™", is sprayed into the exhaust gas stream upstream of the catalyst In the SCR catalyst, in a first step, a hydrolysis of the urea solution to ammonia and in a second step, a reaction of ammonia and NOx to water and nitrogen.

From DE 103 23 607 A1, WO 2005/016497 and US 2011/0078997 catalysts are known which have a combination of an SCR catalyst and a particle filter on a single substrate. These catalysts are commonly referred to as SCRF catalysts (SCR on filters) and can both trap soot particles and reduce nitrogen oxides NOx to nitrogen.

DE 10 2012 209 852 A1 shows a catalyst arrangement in which an SCRF system is expanded downstream by an SCR catalyst, wherein the SCR catalyst has an additional storage function for hydrocarbons. Downstream of the SCR catalyst is an oxidation catalyst which can oxidize the hydrocarbons and carbon monoxide. DE 10 2009 038 835 A1 discloses an exhaust gas purification system comprising a first SCR catalyst upstream of an oxidation catalyst and a particulate filter and another SCR catalyst downstream of the particulate filter. From DE 10 2011 079 785 an exhaust system is known, in which a first oxidation catalyst (DOC) is provided, behind which an SCR device and a second DOC is arranged in the flow direction of the exhaust gas. With this system lower hydrocarbon emissions are to be achieved. The SCR device can be supplemented by a downstream SCRF catalyst.

The cited catalyst arrangements are designed to comply with the increasingly stringent limit values for nitrogen oxide and hydrocarbon pollution in exhaust gases of internal combustion engines.

A disadvantage of the close-coupled SCRF catalysts, however, is that the component volume of the SCRF catalyst is increased compared to the previously used, coated with noble metal and also referred to as "Coated Soot Filter" (CSF) particulate filters were design parameters for the CSF in the past, the so-called "ash storage capacity" and the maximum exhaust gas mass flow of the internal combustion engine. For the SCRF catalyst, the NOx conversion must also be considered, which leads to a larger component volume. However, the larger component volume of the SCRF catalyst requires increased weight, increased costs, and increased thermal inertia.

The object of the present invention is to provide a reliable and cost-effectively producible in all operating situations emission control system, with which the above disadvantages can be avoided.

The invention is achieved by a catalyst assembly for a device for purifying exhaust gases of an internal combustion engine, in particular a diesel engine, according to claim 1. Advantageous embodiments of the invention are specified in the subclaims, which can be optionally combined with each other. According to the invention, the catalyst assembly comprises a regenerable particulate filter and a catalyst for the selective reduction of nitrogen oxides (SCRF catalyst) integrated on the particulate filter. Upstream of the SCRF catalyst, a catalyst for the selective reduction of nitrogen oxides (SCR catalyst) is provided, wherein the SCRF catalyst and the SCR catalyst are arranged in a common catalyst housing.

The core of the invention is thus a hybrid construction comprising an SCR catalyst on its own carrier substrate and a downstream SCRF catalyst with a component volume which corresponds to the volume of a customary for each variant of the internal combustion engine CSF. This hybrid design has the advantage that a modular system can be provided for different vehicles in which, depending on the size of the vehicle or engine variant, the SCRF catalysts are dimensioned the same and the dimensions of the SCR catalysts are varied. The preparation of the catalyst assembly can therefore be carried out at a lower cost.

Further advantages of the catalyst assembly according to the invention result from the fact that the SCR catalyst shows a faster light-off behavior of the SCR function in normal operation and a better NOx conversion in the emission cycle due to its lower thermal inertia. This results in an improved efficiency of the catalyst assembly with the same total volume. Due to the smaller volume of the particulate filter also results in a lower total weight. In addition, the cost of the hybrid system is lower because the SCR catalyst can be made cheaper than a particulate filter. In the regeneration mode of the particulate filter, the heating of the assembly due to ^" the lower heat capacity of the SCR filter can be done faster.

According to a preferred embodiment, the SCR catalyst comprises a metallic or ceramic flow-through substrate. The flow-through substrate is typically a honeycomb monolith having a series of elongate channels extending therethrough, with the channels open at both ends. Such a flow-through substrate can be manufactured at low cost with different axial dimensions. In this way, the NOx conversion of the SCR catalyst can be easily adapted to different engine variants be adjusted. The differences in the various axial dimensions are greater than the manufacturing tolerances usually encountered in the production of substrate monoliths for catalysts.

The SCRF catalyst is preferably formed as a filtering monolith, more preferably as a wall-flow filter, for example in the form of a ceramic porous filter substrate, comprising a plurality of inlet channels arranged parallel to one another and a plurality of outlet channels, each inlet channel and each Outlet channel is partially defined by a ceramic wall of a porous structure. Each inlet channel is alternately separated from an outlet channel by a ceramic wall of a porous structure and vice versa. In other words, the wall-flow filter is a honeycomb arrangement defining a plurality of first channels closed at the upstream end and a plurality of second channels not sealed at the upstream end but closed at the downstream end. Channels that are vertically and laterally adjacent to a first channel are closed at the downstream end. When viewed from one of the ends, the alternately closed and open ends of the channels have the appearance of a chessboard.

The SCRF catalyst can be formed as a bulk extrudate or as a coated carrier substrate. Suitable catalytically active substances include mixed oxides of vanadium and titanium, iron- and copper-containing zeolites and mixtures thereof.

The flow-through substrate of the SCR catalyst is preferably a disc-shaped honeycomb monolith, in particular with a substantially cylindrical or polygonal, preferably rectangular cross-section. The geometry of the flow-through substrate is preferably adapted to the external dimensions of the SCRF catalyst.

As the catalytically active component for the SCR catalyst, the conventional coatings and solid extrudates known in the art can be used. Suitable catalysts for the selective reduction of nitrogen oxides include for example, copper-containing compounds, mixed oxides and mixtures of oxides of vanadium oxide and titanium dioxide and optionally tungsten oxide, molybdenum oxide and ^■ silica, iron and copper-containing and acidic Zeoiithe Zeolites, which may be partially exchanged with metal ions, and mixtures thereof.

Particularly preferably, at least one spacer element is provided between the SCR catalyst and the SCRF catalyst or an axial wall surface of the catalyst housing. With the spacer elements, the different axial expansions of the SCR catalyst can be compensated for the same volume of the catalyst housing and the SRCF catalyst. As spacers fixed spacers and / or nonwovens, knitted fabrics and fabrics can serve, which are usually also used to compensate for manufacturing tolerances of the catalyst substrates. Preference is given to heat-resistant wire knits.

The invention further relates to a modular system for the catalyst assembly according to claim 5.

The modular system according to the invention is used for a plurality of variants of an internal combustion engine, in particular a diesel engine, and comprises a plurality of catalytic converter housings and SCRF catalytic converters, which are dimensioned independently of the engine variant for the various variants of the internal combustion engine, and a set of a plurality of different SCR catalytic converters, which are dimensioned for the plurality of ^'variants of the internal combustion engine, respectively in dependence on the engine type and having different outer dimensions.

Preferably, the SCRF catalysts and the catalyst housing of the modular system each have the same outer dimensions, which are suitable for use with multiple engine variants. Preferably, the catalyst housing and the SCRF catalysts in the kit each have an equal volume and / or an equal ratio of length to cross section.

Equal external dimensions or an equal volume or an equal ratio of length to cross section mean here that the dimensions of the SCRF catalysts and / or the catalyst housing in the modular system vary only within the usual manufacturing tolerances. The adaptation to several engine variants takes place by optimization and definition of the dimensions dimensioning of the catalyst housing and of the SCRF catalytic converter, so that for all engine variants of the modular system without additional SCR

Catalyst sufficient pollutant reduction is achieved in compliance with predetermined limits. The dimensions of the plurality of SCR catalysts in the modular system are preferably selected so that the respective SCR catalytic converter has an axial extent adapted to the associated engine variant and optionally the dimensions of the SCRF catalytic converter. By selecting the SCR catalytic converter with the axial extent suitable for the respective engine variant, it is then possible in particular to lower the nitrogen oxides in the exhaust gas stream to values below the legal limit values.

In addition, the modular system may include a set of different spacers adapted to the sizing of the plurality of SCR catalysts. Since differently dimensioned SCR catalysts are used depending on the engine variant, it is thus possible to compensate for any voids that may be formed in the catalyst housing. The spacer elements may be fixed spacers such as spacer rings, or it may be used with different wall thicknesses also used to compensate for manufacturing tolerances heat-resistant wire mesh.

The invention further comprises an apparatus for purifying exhaust gases of an internal combustion engine with the catalyst assembly according to the invention according to claim 10.

In particular, the apparatus may include means for supplying a reductant, particularly ammonia or an ammonia precursor, located upstream of the catalyst assembly. The reducing agent is preferably a urea solution commercially available as "AdBlue ™" whose composition is internationally standardized Downstream of the means for supplying the reducing agent and upstream of the catalyst assembly, there may be provided a mixing element or evaporator which provides uniform distribution of the Reducing agent causes in the exhaust stream. Furthermore, the device may comprise a known oxidation catalytic converter and / or a NOx catalytic converter, which are each arranged in the exhaust line upstream of the module and the device for supplying a reducing agent. As another preferred embodiment, the apparatus may include an ammonia trap catalyst downstream of the SCR catalyst and SCRF catalyst assembly disposed downstream of the assembly. The ammonia blocking catalyst prevents the odor nuisance caused by the so-called ammonia slip, which can be caused by overdosing of the reducing agent.

The inventive method for producing the catalyst assembly from a modular system for several variants of an internal combustion engine, in particular a diesel engine, comprises the following steps:

a) providing a plurality of catalyst housings and a plurality of SCRF catalysts each having the same dimensions; b) selecting a SCR catalyst sized according to the respective engine variant from a set of different SCR catalysts; and

c) assembling the selected SCR catalyst with the SCRF catalyst in the catalyst housing to form the

A catalyst assembly.

With the method according to the invention, a modular construction of the catalyst assembly can be realized. Since only the low-cost SCR catalyst is varied, both the warehousing costs and the manufacturing costs of the assembly as a whole can be reduced.

According to another embodiment of the method, the kit additionally contains a set of differently dimensioned compensation elements, wherein at least one compensation element for the respective engine variant is selected as a function of the dimensioning of the SCR catalytic converter from the set of compensation elements and installed in the catalytic converter housing. Further advantages of the invention will become apparent from the following description of a preferred embodiment with reference to the accompanying drawings.

In the drawing, the single figure shows a schematic representation of an apparatus for purifying exhaust gases of an internal combustion engine with the catalyst assembly according to the invention.

The device 10 shown schematically in the figure is used in particular for cleaning the exhaust gases 12 of a diesel engine (not shown) and comprises in the flow direction of the exhaust gases: - a known exhaust gas turbocharger 14;

a known oxidation catalyst 16, wherein the oxidation catalyst may be replaced by a NOx storage catalyst or combined with a NOx storage catalyst;

a known device 18 for supplying a reducing agent for nitrogen oxides, for example a urea solution injection device with a downstream mixing element (not shown);

the catalyst assembly 20 according to the invention; and

a known ammonia blocking catalyst 22, from which the purified waste gases can be released into the environment. Instead of or in addition to the ammonia barrier catalyst, a further SCR catalyst, an oxidation catalyst or a combination of SCR catalyst and oxidation catalyst may be provided, as is known in the art.

The catalyst assembly according to the invention comprises an SCR catalytic converter 24 and a downstream SCRF catalytic converter 26 downstream of the SCR catalytic converter.

The SCR catalyst 24 is used for the selective reduction of nitrogen oxides and is preferably designed as a flow-through substrate without a filter function, in particular as a disk-shaped honeycomb monolith. The SCRF catalyst 26 is composed of a regenerable particulate filter and a catalyst for the selective reduction of nitrogen oxides integrated on the particulate filter.

The SCR catalyst 24 and the SCRF catalyst 26 are arranged in a common catalyst housing 28.

According to the invention, the catalyst assembly 20 can be assembled from a modular system. The modular system allows a modular design of the catalyst assembly 20, which can be used for several variants of an internal combustion engine, in particular a diesel engine.

The kit comprises a plurality of catalytic converter housings 28 and a plurality of SCRF catalytic converters 26, which are dimensioned in each case independently of the engine variant for a plurality of variants of the internal combustion engine, i. have the same outer dimensions. As part of the usual manufacturing tolerances deviations are considered here as the same dimensions.

In addition, the kit comprises a set of different SCR catalysts 24, which are dimensioned for the several variants of the internal combustion engine depending on the engine variant.

Preferably, the catalyst housing 28 and the SCRF catalysts 26 in the kit may have an equal volume and / or an equal length to cross-section ratio.

The dimensions of the various SCR catalysts in the modular system are preferably chosen so that the respective SCR catalyst has an adapted to the associated engine variant axial extent and optionally adapted to the outer dimensions of the SCRF catalyst geometry.

In addition, the modular system may include a set of a plurality of different spacers (not shown) adapted to the sizing of the various SCR catalysts. The spacer elements are used to compensate for the voids possibly formed in the catalyst housing, which due to the use of SCR- Catalysts 24 can arise with different dimensions. As spacers fixed spacers such as spacer rings or used to compensate for manufacturing tolerances heat-resistant wire mesh can be used with different wall thicknesses.

For the production of the catalyst assembly 20 according to the invention from the modular system, first a catalyst housing 28 and a SCRF catalyst with predetermined, adapted to the several engine variants dimensions are provided. Subsequently, depending on the particular engine variant, a suitably dimensioned SCR catalyst 24 is selected from a set of SCR catalysts having different dimensions or axial dimensions. The catalyst housing 28, the SCRF catalyst 26, and the SCR catalyst 24 selected from the kit are then installed to the catalyst assembly 20, optionally along with spacers also selected from the kit.

As an example of the dimensioning of the catalyst assembly 20 may be compared with a conventional diesel particulate filter (CSF) for a 2.0 dm ³ diesel engine:

CSF volume = 2.8 dm ³

Maintaining the optimum ratio of length to cross section of the CSF, this results in a volume of 3.5 dm ³ for a SCRF catalyst.

The hybrid system of catalyst assembly 20 composed of an SCR catalyst 24 and a SCRF catalyst 26 may thus have the following volume: volume hybrid system = SCR volume + SCRF volume

= 0.7 dm ³ + 2.8 dm ³ = 3.5 dm ³

For use with another engine variant, the SCRF volume is maintained and only the SCR volume or axial extent of the SCR flow-through substrate is varied. With the modular system according to the invention can thus be realized a cost-effective modular design of the catalyst assembly. At the same time there are also technical advantages, as the SCR flow-through substrate has a lower heat capacity and a better thermal Anspringverhaiten shows. In addition, with the same total volume, the efficiency of the catalyst assembly can be improved because the NOx conversion of the SCR catalyst is greater.

Claims

claims

Catalyst assembly (20) for a device (10) for cleaning exhaust gases of an internal combustion engine, in particular a diesel engine, with a regenerable particulate filter and a particulate filter integrated on the catalyst for the selective reduction of nitrogen oxides (SCRF catalyst) (26) in that a catalyst for the selective reduction of nitrogen oxides (SCR catalyst) (24) is provided upstream of the SCRF catalytic converter (26), and the SCRF catalytic converter (26) and the SCR catalytic converter (24) are housed in a common catalytic converter housing ( 28) are arranged.

2. Catalyst assembly (20) according to claim 1, characterized in that the SCR catalyst (24) comprises a metallic or ceramic flow substrate.

3. Catalyst assembly (20) according to any one of claims 1 or 2, characterized in that the flow-through substrate is a disk-shaped honeycomb monolith.

4. Catalyst assembly (20) according to any one of claims 1 or 2, characterized in that at least one spacer element between the SCR catalyst (24) and the SCRF catalyst (26) or an axial wall surface of the catalyst housing (28) is provided.

5. Modular system for a catalyst assembly (20) according to one of claims 1 to 4 for use for several variants of a combustion ^• engine, in particular a diesel engine, with a plurality of catalyst housings (28) and SCRF catalysts (26), for the several variants of the internal combustion engine are each dimensioned independently of the engine variant, and a set of different SCR catalysts (24), which are dimensioned for the several variants of the internal combustion engine depending on the engine variant and have different outer dimensions.

6. Modular system according to claim 5, characterized in that the SCRF catalysts (26) of the modular system have an equal ratio of length to cross section.

7. Modular system according to claim 5 or 6, characterized in that the SCRF catalysts (26) of the modular system have the same external dimensions.

8. Modular system according to one of claims 5 to 7, characterized in that the different SCR catalysts (24) have a different, adapted to the respective engine variant axial extent.

A modular system according to any one of claims 5 to 8, further comprising a set of different spacers adapted to the sizing of the plurality of SCR catalysts (24).

10. Device (10) for purifying exhaust gases of an internal combustion engine with a catalyst assembly (20) according to one of claims 1 to 4.

The apparatus (10) of claim 10, wherein means (18) for supplying a reductant, particularly ammonia or an ammonia precursor, is disposed upstream of the catalyst assembly (20).

12. Device (10) according to claim 11, wherein an oxidation catalyst (16) and / or a NOx storage catalyst upstream of the catalyst assembly (20) and the means (18) for supplying a reducing agent is arranged.

The apparatus (10) of any one of claims 10 to 12, wherein an ammonia blocking catalyst (22) is disposed downstream of the catalyst assembly.

14. A method for producing a catalyst assembly (20) from a modular system according to one of claims 5 to 9 for use for a plurality of engine variants of an internal combustion engine, in particular a diesel engine, comprising the following steps:

Providing a plurality of catalyst housings (28) and SCRF catalysts (26) each having the same dimensions;

Selecting a SCR catalyst (24) sized according to the respective engine variant from a set of different SCR catalysts; and Assembling the selected SCR catalyst (24) with the SCRF catalyst (26) in the catalyst housing (28) to form the catalyst assembly (20).

15. The method according to claim 14, characterized in that a compensation element depending on the dimensioning of the SCR catalyst (24) is selected from a set of different compensation elements and installed in the catalyst housing (28).